The technical field of this disclosure is location detection systems and methods, particularly, location detection systems and methods with fingerprinting.
Wireless communication and control networks are becoming increasingly popular for home automation, building automation, healthcare infrastructure, low power cable-less links, asset control, and other applications. One benefit of such networks is the ability to locate a network device or tag. For example, lighting commissioning personnel can quickly identify a specific wireless device, so installation costs can be reduced. Expensive equipment may be tagged, and tracked in and around a building, allowing staff to easily locate the tagged equipment when needed for use, in an emergency, or for calibration. Tagged equipment can also generate an alarm when moved beyond specified boundaries. One example of such a wireless communication and control network is a ZigBee network, which is a low cost, low power, wireless standard using the ZigBee protocol operating on top of the IEEE 802.15.4 wireless standard.
Although wireless devices can be located by estimating the distance from a number of fixed points and triangulating the location from the distance estimates, the accuracy of the location depends on the accuracy of the distance estimates. Two methods of estimating distance are time of flight and signal strength. The distance for a time of flight distance estimate is computed from the time for a signal to pass from one point to another and the expected signal velocity. The distance for a signal strength distance estimate is computed from the decrease in signal strength and the expected signal strength decay. Unfortunately, the bandwidth of some wireless communication and control networks is too narrow to make a time of flight distance estimate. In addition, the signal strength of some wireless communication and control networks varies widely with position due to attenuation and reflection from objects such as walls and people, typically preventing either a time of flight distance estimate or a signal strength distance estimate.
Another approach to location detection has been fingerprinting. Signal strengths are measured over the area of the wireless communication and control network to determine a set of fingerprints for the area, i.e., a map of signal strengths from nearby devices for any location within the area. A device to be located measures the signal strength from the devices at known locations around it. The measured signal strengths are compared to the set of fingerprints to determine the location of the device. Unfortunately, determining the set of fingerprints of the area is time and labor intensive, making the process expensive. Also, the comparison between the measured signal strengths and the set of fingerprints requires comparison over the whole set of fingerprints, requiring a great deal of computational effort and time.
It would be desirable to have a location detection system and method with fingerprinting that would overcome the above disadvantages.